Use the commit-queue data structure to implement a priority queue
of commits sorted by committer date, when handling --date-order.
The commit-queue structure can also be used as a simple LIFO stack,
which is a good match for --topo-order processing.

Signed-off-by: Junio C Hamano <gits...@pobox.com>
---
 commit-queue.c | 13 +++++++++++
 commit-queue.h |  3 +++
 commit.c       | 74 ++++++++++++++++++++++++++++++++++------------------------
 3 files changed, 59 insertions(+), 31 deletions(-)

diff --git a/commit-queue.c b/commit-queue.c
index 77d4b02..ffffc4e 100644
--- a/commit-queue.c
+++ b/commit-queue.c
@@ -2,6 +2,19 @@
 #include "commit.h"
 #include "commit-queue.h"
 
+void commit_queue_reverse(struct commit_queue *queue)
+{
+       int i, j;
+
+       if (queue->compare != NULL)
+               die("BUG: commit_queue_reverse() on non-LIFO queue");
+       for (i = 0; i <= (j = (queue->nr - 1) - i); i++) {
+               struct commit *swap = queue->array[i];
+               queue->array[i] = queue->array[j];
+               queue->array[j] = swap;
+       }
+}
+
 void clear_commit_queue(struct commit_queue *queue)
 {
        free(queue->array);
diff --git a/commit-queue.h b/commit-queue.h
index 7c5dc4c..d3c92e5 100644
--- a/commit-queue.h
+++ b/commit-queue.h
@@ -28,4 +28,7 @@ extern struct commit *commit_queue_get(struct commit_queue *);
 
 extern void clear_commit_queue(struct commit_queue *);
 
+/* Reverse the LIFO elements */
+extern void commit_queue_reverse(struct commit_queue *);
+
 #endif /* COMMIT_QUEUE_H */
diff --git a/commit.c b/commit.c
index fc1734b..46cd150 100644
--- a/commit.c
+++ b/commit.c
@@ -9,6 +9,7 @@
 #include "gpg-interface.h"
 #include "mergesort.h"
 #include "commit-slab.h"
+#include "commit-queue.h"
 
 static struct commit_extra_header *read_commit_extra_header_lines(const char 
*buf, size_t len, const char **);
 
@@ -504,21 +505,41 @@ struct commit *pop_commit(struct commit_list **stack)
 
 define_commit_slab(indegree_slab, int);
 
+static int compare_commits_by_commit_date(struct commit *a, struct commit *b, 
void *unused)
+{
+       /* newer commits with larger date first */
+       if (a->date < b->date)
+               return 1;
+       else if (a->date > b->date)
+               return -1;
+       return 0;
+}
+
 /*
  * Performs an in-place topological sort on the list supplied.
  */
-void sort_in_topological_order(struct commit_list ** list, enum rev_sort_order 
sort_order)
+void sort_in_topological_order(struct commit_list **list, enum rev_sort_order 
sort_order)
 {
        struct commit_list *next, *orig = *list;
-       struct commit_list *work, **insert;
        struct commit_list **pptr;
        struct indegree_slab indegree;
+       struct commit_queue queue;
+       struct commit *commit;
 
        if (!orig)
                return;
        *list = NULL;
 
        init_indegree_slab(&indegree);
+       memset(&queue, '\0', sizeof(queue));
+       switch (sort_order) {
+       default: /* REV_SORT_IN_GRAPH_ORDER */
+               queue.compare = NULL;
+               break;
+       case REV_SORT_BY_COMMIT_DATE:
+               queue.compare = compare_commits_by_commit_date;
+               break;
+       }
 
        /* Mark them and clear the indegree */
        for (next = orig; next; next = next->next) {
@@ -528,7 +549,7 @@ void sort_in_topological_order(struct commit_list ** list, 
enum rev_sort_order s
 
        /* update the indegree */
        for (next = orig; next; next = next->next) {
-               struct commit_list * parents = next->item->parents;
+               struct commit_list *parents = next->item->parents;
                while (parents) {
                        struct commit *parent = parents->item;
                        int *pi = indegree_slab_at(&indegree, parent);
@@ -546,30 +567,28 @@ void sort_in_topological_order(struct commit_list ** 
list, enum rev_sort_order s
         *
         * the tips serve as a starting set for the work queue.
         */
-       work = NULL;
-       insert = &work;
        for (next = orig; next; next = next->next) {
                struct commit *commit = next->item;
 
                if (*(indegree_slab_at(&indegree, commit)) == 1)
-                       insert = &commit_list_insert(commit, insert)->next;
+                       commit_queue_put(&queue, commit);
        }
 
-       /* process the list in topological order */
-       if (sort_order != REV_SORT_IN_GRAPH_ORDER)
-               commit_list_sort_by_date(&work);
+       /*
+        * This is unfortunate; the initial tips need to be shown
+        * in the order given from the revision traversal machinery.
+        */
+       if (sort_order == REV_SORT_IN_GRAPH_ORDER)
+               commit_queue_reverse(&queue);
+
+       /* We no longer need the commit list */
+       free_commit_list(orig);
 
        pptr = list;
        *list = NULL;
-       while (work) {
-               struct commit *commit;
-               struct commit_list *parents, *work_item;
-
-               work_item = work;
-               work = work_item->next;
-               work_item->next = NULL;
+       while ((commit = commit_queue_get(&queue)) != NULL) {
+               struct commit_list *parents;
 
-               commit = work_item->item;
                for (parents = commit->parents; parents ; parents = 
parents->next) {
                        struct commit *parent = parents->item;
                        int *pi = indegree_slab_at(&indegree, parent);
@@ -582,27 +601,20 @@ void sort_in_topological_order(struct commit_list ** 
list, enum rev_sort_order s
                         * when all their children have been emitted thereby
                         * guaranteeing topological order.
                         */
-                       if (--(*pi) == 1) {
-                               switch (sort_order) {
-                               case REV_SORT_BY_COMMIT_DATE:
-                                       commit_list_insert_by_date(parent, 
&work);
-                                       break;
-                               default: /* REV_SORT_IN_GRAPH_ORDER */
-                                       commit_list_insert(parent, &work);
-                                       break;
-                               }
-                       }
+                       if (--(*pi) == 1)
+                               commit_queue_put(&queue, parent);
                }
                /*
-                * work_item is a commit all of whose children
-                * have already been emitted. we can emit it now.
+                * all children of commit have already been
+                * emitted. we can emit it now.
                 */
                *(indegree_slab_at(&indegree, commit)) = 0;
-               *pptr = work_item;
-               pptr = &work_item->next;
+
+               pptr = &commit_list_insert(commit, pptr)->next;
        }
 
        clear_indegree_slab(&indegree);
+       clear_commit_queue(&queue);
 }
 
 /* merge-base stuff */
-- 
1.8.3-451-gb703ddf

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